Extrusion of tubular shapes of aluminum and alloys thereof



Nov. 1, 1938. w. s. UNDERHILL Filed June 21, 1935 Patented Nov. 1, 1938 PATENT OFFICE EXTRUSION OF TUBULAR SHAPES OF ALU- MINUM AND ALLOYS THEREOF Wyvel 8. Under-hill, Detroit, Mich, assignmto Aluminum Company of America, Pittsburgh, Pa., a corporation of Pennsylvania Application June 21, 1935, Serial No. 27,84;

comm.

This invention relates to the formation of tubular shapes of aluminum and of aluminum alloys by extrusion, and its chief object is to provide an improved method and apparatus by s which tubular articles or shapes can be extruded at high speed with accurately finished inner and outer surfaces and without unwanted variations or irregularities in wall thickness. Heretofore the common practice has been to form the longitudinal hollow or bore by means of a floating" mandrel or core. In that method a pierced billet is used, that is, one provided with a longitudinal bore, and the mandrel, in the form of a rod with a slight taper, is mounted loosely on the piston or plunger and extends into the bore of the billet, which bore is aligned with the die at the forward end of the cylinder so that the end of the mandrel extends into the die. Then as the piston advances, the metal is forced out through the annular space between the wall of the die opening and the surface of the mandrel,

which extends through the die opening and advances at the same rate as the forward movement of the piston. It is assumed that with the 5 billet fitted closely to the cylinder and the bore accurately aligned with the die opening, the

radial pressures exerted by the metal upon the floating mandrel will be equal in all directions,

thereby keeping the mandrel accurately posi- 30 tioned in the die opening at all times. In practice, however, this condition of equal pressures is rarely, if ever, obtained, with the result that the mandrel shifts radially of the cylinder as it advances, thus producing variations in the wall 35 thickness of the article. To avoid the defect of variation in wall thickness incident to the use of a floating mandrel it has been proposed to mount the mandrel or core rigidly by means of a longitudinal fin terminating short of the die 40 opening itself but permitting the core to extend into the die opening; the idea being that although the metal is divided by the core supporting an as it flows toward the die opening the two edges will unite in the space around the core immediately 45 back of the die opening, after which the metal will be forced through the annular space between the wall of the die opening and the surface of the core.

In the course of my experience with cores rigid- 50 ly supported in the adapter I have found that for ease of working, uniformly high quality of products, and extrusion at speeds comparable to those obtainable with a floating mandrel, the die structure should have certain features, as follows:

55 The passage or passages, preferably two or more,

through which the metal flows to the space or chamber in which the streams expand and coalesce or weld together, should have a forward spread or flare, and their rear orifices, through which the metal enters the passages, should have 5 shearing edges, so that the metal is formed into streams in part, at least, by a shearing action rather than wholly by a molding or compressing action. The welding space or chamber, between the die opening and the adapter passages, should in not taper forwardly, as if to progressively crowd the metal radially inward toward the core and the die opening. Preferably the chamber has a pronounced forward flare. The orifice of the die opening, through which orifice the metal en- 15 ters the die opening, should have a shearing edge, and the core should also have a circumferential shearing edge, located substantially in the same plane as the shearing edge of the die opening, so that the metal will be sheared, at least in part. 20 into space between the core and the wall of the die opening. Beyond these shearing edges the metal should, in general, have quick relief, that is, it should pass promptly out of contact with the die surfaces.

Referring now to the accompanying drawing, in which I have shown a form of the invention designed to produce a cylindrical pipe:

Fig. l is a longitudinal section showing the extrusion cylinder and plunger, and a die structure embodying my invention in convenient and efficient form.

Fig. 2 is an end view of the adapter", from the right of Fig. 1.

Fig. 3 is a cross section of the adapter, on the line 33 of Fig. 1.

Fig. 4 is a longitudinal section on the line 4-4 of Fig. 2.

The extrusion cylinder and the plunger are shown, somewhat diagrammatically, at Ill and ll, respectively. In the embodiment illustrated the die structure is composed of two parts, one, marked i2, I call the adapter. The other is a die plate l3. The adapter is cylindrical in form, fltted tightly to the forward or exit end of the extrusion cylinder, and carries the mandrel or core II by means of four radial fins or supports i5, symmetrically arranged and providing between them four passages, l6, through which metal flows forwardly under the pressure of the plunger.

The adapter is preferably made of a single piece, as it is diilicult to obtain adequate strength in a built up device. The passages i6 through which the metal flows to the die flare forwardly 5s and their entrance orifices are formed with shearing edges If. These edges are preferably sharp, but a slight rounding or chamber is permissible to lessen chipping or wear. Or the face of the adapter may be slightly dished around the passages.

It is desirable that as the billet (not shown) is advanced to shear the metal into the passages iii, the metal which is actually in contact with the rear face of the die structure does not move on such face but that the radial flow of the metal toward the passage takes place in rear of the billet face. That is to say, for the best results the flow should be wholly inside of the billet. For this reason any forward coning or tapering of the rear face of the die structure toward the passages l8 should be insumclent to permit any such slippage or movement, and I therefore prefer to make the rear face of the die structure flat or substantially so and at right angles to the axis of the cylinder.

At their forward ends the passages I8 open into an annular space or chamber l8 (around the free or unsupported forward portion of the core II) in which the metal streams coalesce or weld to gether. This chamber is preferably formed with a forward flare toward its front wall, which in the present instance is the rear face of the die plate l3. The latter is fitted tightly to the front of the adapter and centered thereon in any convenient way, as by means of a rib and groove as indicated at i9. \By preference the front wall of the chamber is substantially flat and at right angles to the die.

The die plate i3 is provided with a die-opening, into which the free or unsupported end of the mandrel or core ll extends to form the annular space through which metal passes from the welding chamber l8. At the rear face of the die plate the opening is formed with a narrow (l. e., axially short) flange 20 providing a rear shearing edge 2|. Beyond the flange the opening in the die plate flares slightly in the forward direction, as indicated in Fig. 1.

The forward end of the core I l is formed with a circumferential flange 22, providing a rear shearing edge 23 preferably in the plane of the shearin edge 2! around the opening in the die plate I3. The two flanges should be narrow, in general no thicker than enough to give any necessary or desired smoothing effect on the inner and outer surfaces of the tubular article. If the flange 20 is omitted the inner surface in front of the shearing edge 2| may be parallel to the axis of the die for an equivalent distance. It is in general important that after being shaped by the shearing edges, and any necessary or desired smoothing by the die surfaces beyond these edges, the metal have immediate relief, that is, pass out of contact with the die. For a pipe having an inside diameter of an inch and three-eighths and a wall thickness of about a quarter of an inch, a flange thickness (measured axially) of about an eighth of an inch is satisfactory. In general the axial thickness need not exceed about one tenth of the inner diameter of the tubular article and in the case of large pipe it can often be much less.

I have not indicated any means for holding the die structure parts together or the whole in place at the end of the cylinder, as any suitable means may be employed for the purpose, preferably such as will permit easy detachment.

In operation, the first effect of the advancing plunger is to form rods of metal at the shearing edges ll of the passages I5. Meeting the front wallofthechamber ll theadvancingrodsare arrested and thereafter expand in the chamber and in the feed es as more and more metal is fed into the latter by the pressure of the plum:- er. When the feed es and welding chamber are full the continued pressure of the plunger shears the metal into tubular form at the die shearing edges II, 28. As the operation proceeds the billet advances as a whole and the passages Ii and welding chamber II are kept full. As the billet advances, its curved surface slides over the inner curved surface of the cylinder, but at the rear face of the die structure there appears to be no slip or movement of the metal which is in contact with the rear face of the die structure. on the contrary, the radial flow of the metal (inwardly from the longitudinal surface and outwardly from the axis of the billet) toward the orifices of the passages l6 takes place in rear of the forward face of the billet, that is to say, inside of the billet. The same is true of the metal in the welding chamber, with respect to the front face of the latter.

It is to be understood that the invention is not limited to the embodiment herein specifically lllustrated and described but can be embodied in other forms without departure from its spirit as defined by the appended claims. Nor is the invention limited to the extrusion of shapes of circular cross section, inside or outside or both, but can be employed in forming other shapes, regular and irregular.

I claim:

1. Method of extruding tubular shapes of aluminum and alloys thereof, comprising pressing a billet of aluminum or an alloy thereof against a surface having one or more shearing-edged openings to form thereby one or more streams of metal; continuing the pressure on the billet and thereby delivering the streams into a welding space and against a surface having an annular opening formed by inner and outer shearing edges; and continuing the pressure to force the metal from the welding space out through the said annular opening and thereby form a tubular shape.

2. Method of extruding tubular shapes of alumlnum and alloys thereof, comprising applying pressure upon a billet of the metal to cause the same to flow under the influence of the applied pressure, providing shearing means disposed substantially normal to the direction of flow of the metal to form one or more streams of the metal, arresting the forward progress of the stream or streams to expand and coalesce the metal, and continuing the pressure to force the coalesced metal through an aperture defined between exterior and interior shearing means, whereby a tubular shape is formed.

3. Method of extruding tubular shapes of aluminum and alloys thereof, comprising pressing a billet of aluminum or an alloy thereof against a substantially flat surface having one or more shearing-edged apertures to form thereby one or more streams of metal; continuing the pressure on the billet and thereby delivering the streams into a coalescing and welding chamber and against a surface having an opening formed by inner and outer shearing edges; and continuing the pressure to force the metal from the welding space out through the said opening to thereby form a tubular shape.

4. Method of extruding aluminum and alloys thereof, comprising pressing a billet of the metal against a substantially flat surface having one or more forwardly extending, forwardly flaring passages to form thereby one or more streams of metal, continuing the pressure on the billet and thereby delivering the stream or streams into a welding and coalescing space, arresting the flow of the stream or streams to completely fill the passages and welding space, and continuing the pressure to force the metal from the welding space out through an aperture defined between an opening in a. surface enclosing the welding space and a core member extending into said opening, whereby a tubular shape is formed.

5. Method of extruding aluminum and alloys thereof, comprising pressing a billet against a substantially fiat surface provided with one or more forwardly extending, forwardly flaring passages leading therefrom and terminating in a welding chamber to form thereby one or more streams of metal, continuing the pressure and thereby delivering the stream or streams against a substantially flat surface forming a wall of the welding chamber to arrest forward movement of the stream or streams and thereby completely flll the passages and welding chamber with metal, and continuing the pressure on the billet to force the metal from the welding chamber through an annular aperture defined between a shearingedged openlng in the substantially flat surface of the welding chamber and a core extending into said opening and having a shearing edge lying in the plane of substantially fiat surface of the welding chamber, whereby a tubular shape is formed.

6. An extrusion-die structure comprising, in combination, an adapter element, and a die plate; said adapter element having a substantially flat rear face and one or more forwardly flaring passages extending forwardly through the adapter and terminating in an expansion chamber, and a core secured to said adapter and extending into the expansion chamber, said core having a circumferential flange at its unsupported extremity; the die plate having a substantially flat rear face in abutting relationship with the adapter, said rear face forming a wall of the expansion chamber, and a die aperture in the die plate into which the aforementioned core extends, said core and die aperture cooperating to define therebetween an axially short passage having parallel walls; said adapter element and die plate being provided with aligning means which permit separation of the adapter and die plate irrespective of unextruded metal Within the adapter following an extrusion operation.

WYVEL S. UNDERHILL.

CERTIFICATE OF CORRECTION Patent No 2,15 5,191

November 1 1958 WYV'EL S. UNDERHILL.

It is hereby certified that error appears in the print d specification of the above numbered patent requiring correction as follows: Page 2, first column, line 5, for the word "chamber" read chamfer;

and that the said Letters Patent shouldbe read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 27th day of December, A. D. 1958.

(Seal) Henry Van Arsdale Acting Commissioner of Patents,

more forwardly extending, forwardly flaring passages to form thereby one or more streams of metal, continuing the pressure on the billet and thereby delivering the stream or streams into a welding and coalescing space, arresting the flow of the stream or streams to completely fill the passages and welding space, and continuing the pressure to force the metal from the welding space out through an aperture defined between an opening in a. surface enclosing the welding space and a core member extending into said opening, whereby a tubular shape is formed.

5. Method of extruding aluminum and alloys thereof, comprising pressing a billet against a substantially fiat surface provided with one or more forwardly extending, forwardly flaring passages leading therefrom and terminating in a welding chamber to form thereby one or more streams of metal, continuing the pressure and thereby delivering the stream or streams against a substantially flat surface forming a wall of the welding chamber to arrest forward movement of the stream or streams and thereby completely flll the passages and welding chamber with metal, and continuing the pressure on the billet to force the metal from the welding chamber through an annular aperture defined between a shearingedged openlng in the substantially flat surface of the welding chamber and a core extending into said opening and having a shearing edge lying in the plane of substantially fiat surface of the welding chamber, whereby a tubular shape is formed.

6. An extrusion-die structure comprising, in combination, an adapter element, and a die plate; said adapter element having a substantially flat rear face and one or more forwardly flaring passages extending forwardly through the adapter and terminating in an expansion chamber, and a core secured to said adapter and extending into the expansion chamber, said core having a circumferential flange at its unsupported extremity; the die plate having a substantially flat rear face in abutting relationship with the adapter, said rear face forming a wall of the expansion chamber, and a die aperture in the die plate into which the aforementioned core extends, said core and die aperture cooperating to define therebetween an axially short passage having parallel walls; said adapter element and die plate being provided with aligning means which permit separation of the adapter and die plate irrespective of unextruded metal Within the adapter following an extrusion operation.

WYVEL S. UNDERHILL.

CERTIFICATE OF CORRECTION Patent No 2,15 5,191

November 1 1958 WYV'EL S. UNDERHILL.

It is hereby certified that error appears in the print d specification of the above numbered patent requiring correction as follows: Page 2, first column, line 5, for the word "chamber" read chamfer;

and that the said Letters Patent shouldbe read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 27th day of December, A. D. 1958.

(Seal) Henry Van Arsdale Acting Commissioner of Patents, 

